Though on the face of it the forest cover in Delhi increased from 5.9 per cent in 1999 to cover 7.5 per cent by 2001, people concerned with environmental issues believe there is a need to continue with the afforestation drives with renewed vigour as much of the change could be due to changes in satellite based mapping technology. According to a senior forest official, satellites now provide a 16 metre by 16 metre resolution as against images which took larger areas into consideration, so even clusters of vegetation now get noticed.